The present invention relates to a vacuum pump that drives a gas transferring body in a pump chamber by rotation of a rotary shaft so as to transfer gas to generate vacuum action.
In a screw type vacuum pump disclosed in Unexamined Japanese Patent Publication No. 10-184576, an exhaust unit having a smaller displacement volume than the vacuum pump is connected to an exhaust region of the vacuum pump. The exhaust unit lowers pressure in the exhaust region of the vacuum pump. Namely, the exhaust unit prevents gas in the exhaust region from flowing back to a closed space in the vacuum pump. This prevention reduces a power loss of the vacuum pump so that power consumption is reduced on the vacuum pump.
An unwanted feature is that the exhaust unit is driven by an additional drive source that differs from a drive source of the vacuum pump. Since the additional drive source is provided for driving the exhaust unit, the size of the vacuum pump becomes relatively large. In addition, manufacturing costs for the vacuum pump increase. Therefore, there is a need for a vacuum pump that reduces power consumption without increasing the size of the vacuum pump and the manufacturing costs.